Method for operating a drive train of a vehicle

ABSTRACT

A method for operating a drive-train ( 1 ) of a vehicle, in particular a municipal or agricultural utility vehicle, which has at least one drive machine ( 2 ), a vehicle transmission ( 3 ) with at least two gears, at least one driven axle ( 8 ) and at least one power take-off ( 10 ). A normal power level is supplied by the drive machine ( 2 ), which is controlled or regulated in accordance with a normal torque characteristic curve ( 18 ). An operating-situation-dependent manner additional power can be supplied to the at least one driven axle ( 8 ) and/or to the at least one power take-off ( 10 ). The additional power supplied is controlled or regulated in accordance with operating-situation-dependent torque characteristic curves ( 18, 19   a  to  19   d,    20   a  to  20   d ) which are called up as a function of the gear selected at the time.

This application claims priority from German Application Serial No. 10 2019 200 125.4 filed Jan. 8, 2019.

FIELD OF THE INVENTION

The invention relates to a method for operating a drive-train of a vehicle, in particular a municipal or agricultural utility vehicle having at least one drive machine, a vehicle transmission with at least two gears, at least one driven axle and at least one power take-off, wherein from the drive machine a normal power level is delivered which is controlled or regulated in accordance with a normal torque characteristic, wherein depending on the operating situation additional power is delivered to the at least one driven axle and/or to the at least one power take-off. In addition the invention relates to a control unit designed to carry out the method and to a corresponding computer program product.

BACKGROUND OF THE INVENTION

In a vehicle drive-train, particularly of municipal or agricultural utility vehicles, the vehicle transmission is an assembly which limits the power delivered by the drive machine. Whereas for a defined power range of vehicles belonging to different power categories a drive machine that covers the power range is used, the vehicle transmissions are designed specifically for each power category.

If a vehicle is designed with a so-termed power-boost function, i.e. a function for calling up additional power, then depending on the operating situation of the vehicle transmission additional power is made available at least temporarily in the area of the drive machine for particular operating situations provided that the vehicle transmission will not be overloaded due to the additional power delivered. For example, a power-boost function is activated during a so-termed PTO (Power Take-Off) operation or during a transport operation of an agricultural vehicle, such as a tractor. In that case, during PTO operation of a tractor for example, a power take-off in the form of a cardan shaft is connected to the drive-train of the tractor in order to be able to drive an auxiliary consumer functionally connected to the cardan shaft. In such a case the drive machine is controlled by means of torque characteristics which are stored in and used by a control unit associated therewith. During normal operation of the drive machine, i.e. when the power-boost function has not been activated, a normal power level corresponding to the design of the vehicle transmission is delivered, which is controlled or regulated in accordance with a normal torque characteristic. When the power-boost function is actuated, additional power is delivered by the drive machine so that the power delivered temporarily is greater than the normal power.

A method of the type mentioned at the start is known from DE 10 2005 001 526 A1.

SUMMARY OF THE INVENTIONS

Beginning from the prior art described above, the purpose of the present invention is now to develop further a method for operating a drive-train of a vehicle, which enables a more efficient mode of operation when the supply of additional power is activated.

From the process-technological standpoint this objective is achieved with the characterizing features of the independent claim(s). A control unit and a computer program product are also the objects of the independent claims. The dependent claims that follow in each case describe advantageous further developments of the invention.

According to the invention, a method is proposed for operating a drive-train of a vehicle, in particular a municipal or agricultural utility vehicle. The drive-train comprises at least one drive machine, a vehicle transmission with at least two gears, at least one driven axle and at least one power take-off. The output side of the drive machine delivers a normal power level, which is controlled or regulated in accordance with a normal torque characteristic, whereas depending on the operating situation additional power can be delivered to the at least one driven axle and/or to the at least one power take-off. For a more efficient mode of operation when the supply of additional power is activated, according to the invention it is provided that the additional power supplied is controlled or regulated in accordance with operation-situation-dependent torque characteristics which are called up as a function of the gear selected at the time. With each gear is associated at least one specific torque characteristic, with reference to which the drive machine is controlled or regulated. This has the advantage that in each case the additional power supplied by the drive machine, which is delivered to the vehicle transmission, is matched to the power capacity of the gear concerned. In particular, components of the lowest gear or gears of the vehicle transmission, i.e. especially gearwheels and bearings, limit the additional power which the vehicle transmission can receive on its input side from the drive machine without damage to the vehicle transmission. Thanks to the present invention it is ensured that when additional power is called for, at most just that amount of power is supplied which each individual gear is capable of transmitting by virtue of its dimensions. In that way, in any operating situation in which additional power is required the vehicle can be operated at the limit of its power without overloading the drive-train or the vehicle transmission. The gear-dependent control or regulation of the drive machine, therefore, besides optimizing the power, contributes toward increasing the useful life of the drive-train.

Preferably, for the operating-situation-dependent provision of additional power, the operation of the at least one power take-off and a driving speed of the vehicle are monitored. With reference to these criteria, it can be determined which of the torque characteristics is used for the control or regulation of the drive machine.

Then, in an operating situation in which the at least one power take-off is not active and the vehicle is being driven at a driving speed below a driving speed limit, the drive machine is controlled or regulated in accordance with the normal torque characteristic curve regardless of the gear selected. The normal torque characteristic curve can be used without restriction in any operating situation of the vehicle and any available gear of the vehicle transmission when the stated conditions are fulfilled.

Furthermore, in an operating situation of the vehicle in which the at least one power take-off is not active and the vehicle is being operated at a driving speed above a driving speed limit, the drive machine can be controlled or regulated in accordance with a gear-specific transport torque characteristic curve as the operating-situation-dependent torque characteristic curve. The operation of the vehicle with an inactive power take-off but at a driving speed above a driving speed limit generally takes place in the context of a transport journey on firm ground that allows high driving speeds. Reaching a high driving speed presupposes a high rotational speed, i.e. a high gear. Thus, during a transport journey of the vehicle additional power can be called for from the drive machine if the driving speed limit is exceeded, when in each case a gear-specific transport torque characteristic curve is used for the control of the drive machine.

In a preferred further development, in an operating situation of the vehicle in which the at least one power take-off is active and the vehicle is being operated at a minimum driving speed below a driving speed limit, the drive machine can be controlled or regulated in accordance with a gear-specific power take-off torque characteristic curve as the operating-situation-dependent torque characteristic curve. Such an operating situation exists, for example, when operating a working implement or trailer connected to the at least one power take-off and being towed by the vehicle. Due to the movement of the vehicle there is sufficient lubrication of the components of the vehicle transmission, which allows the drive-train to be operated at the limit of its power in the gear concerned, as specified by the respective gear-specific power take-off torque characteristic curve.

In this connection, in an operating situation of the vehicle in which the at least one power take-off is active and the speed of the vehicle is zero, the drive machine can be controlled or regulated in a gear-specific manner in accordance with the power take-off torque characteristic curve with the application of a reduction factor. In this operating situation, in which the vehicle is at rest, the lubrication of the components of the vehicle transmission may not be sufficient to enable the drive-train to be operated at the limit of its power in the gear concerned in accordance with the power take-off torque characteristic curve. By applying the reduction factor to the respective gear-specific power take-off torque characteristic curve, it is ensured that additional power can be called up, such that the torque is above the normal torque characteristic curve but below the respective gear-specific power take-off torque characteristic curve.

According to a preferred embodiment, the vehicle transmission can comprise at least two synchronous gears and at least two powershiftable gears, and when these are selected an operating-situation-dependent, gear-specific torque characteristic curve is called up for the control or regulation of the drive machine. In this case a number of gear-specific torque characteristic curves, i.e. transport torque characteristic curves and power take-off torque characteristic curves, increased by a factor corresponding to the number of powershiftable gears, can be stored in a recoverable manner, by which means the gear-specific supply of the operating-situation-dependent additional power by the drive engine can be adjusted more precisely.

The invention further relates to a control device for controlling a drive train of a vehicle, in particular a municipal or agricultural utility vehicle.

To achieve the objective of the invention stated at the start, according to the independent claim(s) a control unit is provided for controlling a drive-train of a vehicle, in particular a municipal or agricultural utility vehicle comprising at least one drive machine, a vehicle transmission with at least two gears, at least one driven axle and at least one power take-off, wherein the drive machine delivers a normal power level that is controlled or regulated by the control unit in accordance with a normal torque characteristic curve in such a way that additional power can be supplied to the at least one driven axle and/or to the at least one power take-off in an operating-situation-dependent manner. The control unit is designed to control or regulate the additional power supplied in accordance with operating-situation-dependent torque characteristic curves, which are called up as a function of the gear selected.

In particular, the control unit is designed to carry out a method according to one or more of the claim(s). The control unit comprises a memory unit and a computer unit, by means of which the torque characteristic curves that can be stored in the memory unit, namely the normal torque characteristic curve and the gear-specific torque characteristic curves, control the drive machine.

The system according to the invention can also be incorporated as a computer program product with program-code means, in order to carry out a method for the operation of a drive-train of a vehicle according to one or more of the claim(s), when the computer program product is run on a computer or an appropriate computing unit, in particular a control unit according to the claim(s).

The invention is not limited to the combination of features indicated in the independent claims or the claims that depend on them. There are in addition options for combining individual features of the invention, provided that they emerge from the claims, the following description of preferred embodiments of the invention, or directly from the drawings. References in the claims to the drawings by the use of indexes are not intended to restrict the protective scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

An advantageous embodiment of the invention, which will be explained in greater detail below, is illustrated in the drawings, which show:

FIG. 1: A schematic representation of a drive-train of a vehicle;

FIG. 2: As an example, a diagram in which a motor characteristic curve of a drive machine of the drive-train, a normal torque characteristic curve, a transport torque characteristic curve and a power take-off torque characteristic curve of the vehicle transmission are compared;

FIG. 3: As an example, a diagram showing gear-specific transport torque characteristic curves; and

FIG. 4: As an example, a diagram showing gear-specific power take-off torque characteristic curves.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The illustration in FIG. 1 schematically shows a drive-train 1 of a vehicle, in particular a municipal or agricultural utility vehicle, which comprises a vehicle transmission 3. The drive-train 1 can be coupled to a drive machine 2. For that purpose the drive-train 1 shown in FIG. 1 comprises an input shaft 4 of the vehicle transmission 3 which—depending on the specific design of the vehicle transmission 3—can be coupled directly or indirectly, for example by way of a starting element or a starting clutch, to an output shaft 5 of the drive machine 2.

Furthermore, the drive-train 1 comprises an output shaft 6 of the vehicle transmission 3, which is coupled to a differential 7. On the output side, in the drive-train 1 shown here the differential 7 is coupled, via a driven axle 8, to respective wheel drives 9 indicated schematically in FIG. 1 by corresponding tires. Obviously, in other example embodiments more complex drive-trains 1 can be implemented, in which for example more than two wheels can be or are coupled via corresponding wheel drives 9 and/or differentials 7 to the drive motor 2.

The drive-train 1 further comprises a power take-off 10 (PTO=Power Take-Off), which can for example be a power take-off shaft of the vehicle, for example an agricultural machine or a tractor. In the example embodiment of the drive-train 1 shown here, the power take-off 10 branches off from the output shaft 6 of the vehicle transmission 3. This is therefore a rear power take-off shaft. Likewise, in other example embodiments drive-trains 1 can have more then one power take-off 10. For example, this can be appropriate when the working machine concerned is a tractor with a front and/or a rear power take-off shaft.

Moreover the transmission 3 and the drive-train 1 comprise at least one sensor 11, whose function and location are such that input power, input torque and/or input rotational speed of the input shaft 4 of the vehicle transmission 3 can be detected. Thus, the sensor 11 is indirectly or directly a measuring device for determining the power.

In this case the sensor 11 is coupled to a control unit 12. The control unit 12 can for example be a vehicle control computer. By way of a sensor signal 13, the sensor 11 supplies to the control unit 12 the values it determines. The control unit 12 comprises a computer unit 14 and a memory unit 15. The memory unit 15 stores, among other things, torque characteristic curves which are used by the control unit 12 for the control of the drive machine 2, as explained in greater detail below. The control unit 12 transmits corresponding control signals 16 to the drive machine 2. The control unit 12 can also transmit control signals to the vehicle transmission 3.

In the drive-train 1 the vehicle transmission 3 is an assembly which limits the power supplied by the drive machine 2. Whereas for a defined power range of vehicles in different power categories a drive machine that covers the power range is used, the vehicle transmissions are designed specifically for each power category.

The drive machine 2 is controlled by the control unit 12, in which at least one motor characteristic curve 17 is stored. The representation in FIG. 2 shows as an example a diagram in which the motor characteristic curve 17, a normal torque characteristic curve 18, a transport torque characteristic curve 19 and a power take-off torque characteristic curve 20 of the drive machine 2 are compared. The vehicle transmission 3 has at least two synchronous gears and in the present example embodiment four synchronous gears. When no additional power is called for, the drive machine 2 is operated for each selected gear in accordance with the course of the normal torque characteristic curve 18. The torque variation in each of the four synchronous gears corresponds to the course of the normal torque characteristic curve 18.

When a specific rotational speed has been reached, the transport torque characteristic curve 19 and the power take-off torque characteristic curve 20 are located above the normal torque characteristic curve 18. Thus, in an operating-situation-dependent manner operating the drive machine 2 in accordance with the transport torque characteristic curve 19 or the power take-off torque characteristic curve 20 enables a higher drive power to be demanded from the drive machine 2 than is the case when the drive machine 2 is controlled or regulated by means of the power take-off torque characteristic curve 20.

For the operating-situation-dependent provision of additional power, the activation of the at least one power take-off 10 and a driving speed of the vehicle are monitored. On the basis of these criteria it can be determined which of the torque characteristic curves 18, 19, 20 stored in the memory unit 15 is used for controlling or regulating the drive machine 2 by means of the control unit 12.

In an operating situation of the vehicle in which the at least one power take-off 10 is not active and the vehicle is being driven at a speed below a driving speed limit, the drive machine 2 is controlled or regulated in accordance with the normal torque characteristic curve 18 regardless of the gear selected in the vehicle transmission 3. In other words, the normal torque characteristic curve 18 is used in any of the four gears.

In an operating situation of the vehicle in which the at least one power take-off 10 is not active and the vehicle is being driven at a speed above a driving speed limit, the drive machine 2 is controlled or regulated in accordance with the transport torque characteristic curve 19 as the operating-situation-dependent torque characteristic curve.

In an operating situation of the vehicle in which the at least one power take-off 10 is active and the vehicle is being driven at a minimum driving speed below a driving speed limit, the drive machine 2 is controlled or regulated by the control unit 12 in accordance with the power take-off torque characteristic curve 20 as the operating-situation-dependent torque characteristic curve.

In this case it is further differentiated whether, in the operating situation of the vehicle in which the at least one power take-off is active, the driving speed is zero, so that the drive machine 2 is controlled or regulated as a function of the power take-off torque characteristic curve 20, but also with the application of a reduction factor.

If an operating situation occurs in which the control or regulation of the drive machine 2 takes place in accordance with the transport torque characteristic curve 19 or the power take-off torque characteristic curve 20, the designed dimensions of the vehicle transmission 3 impose a power restriction that limits the provision of additional power by the drive machine 2. The gearwheels and bearings at least of the lowest gear limit the power input of the vehicle transmission 3. To optimize the additional power that can be supplied, according to the invention it is provided that the additional power supplied is controlled or regulated in accordance with the operating-situation-dependent torque characteristic curves 18, 19 a to 19 d, 20 a to 20 d, which are called up as a function of the synchronous gear selected at the time. To each of the four synchronous gears is assigned a specific torque characteristic curve 19 a to 19 d and 20 a to 20 d, in accordance with which the drive machine 2 is controlled or regulated, in an operating situation different from normal operation in which additional power should be provided. Thanks to the present invention it is ensured that when additional power is called for, for each synchronous gear selected just that amount of power is supplied by the drive machine 2 and delivered to the vehicle transmission 3 which each individual synchronous gear can at most transmit by virtue of its dimensions. Thus, for example, account is taken of the circumstance that whereas in the lower gears, due to the high gear ratio a very high torque could be transmitted, for reasons of space the gearwheels etc. of the first and often also the second synchronous gear cannot be made arbitrarily large in order to transmit all of the motor power available at any operating point.

This is explained, as an example, with reference to FIGS. 3 and 4. FIG. 3 shows as an example a diagram of gear-specific transport torque characteristic curves 19 a, 19 b, 19 c and 19 d, and FIG. 4 shows as an example a diagram of gear-specific power take-off torque characteristic curves 20 a, 20 b, 20 c and 20 d, each stored in and recoverable from the memory unit of the control unit 12. For reference purposes, FIGS. 3 and 4 also indicate the normal torque characteristic curve 18 which is used in a gear-independent manner for the control or regulation of the drive machine 2 by the control unit 12 when no additional power is called for while the power take-off 10 is being operated, or during a transport journey at high speed.

The gear-specific assignment provides that in an operating situation in which one of the transport torque characteristic curves 19 a to 19 d is used for the control of the drive machine 2, if the first synchronous gear is selected the transport torque characteristic curve 19 a is called up from the memory unit 15. Correspondingly, if the second synchronous gear is selected the transport torque characteristic curve 19 b, if the third synchronous gear is selected the transport torque characteristic curve 19 c and if the fourth synchronous gear is selected the transport torque characteristic curve 19 d is called up. Here, the shape of the transport torque characteristic curve 19 d corresponds to the shape of the transport characteristic curve 19 according to FIG. 2 and describes the maximum transmittable torque. Due to the gear-specific assignment of the transport torque characteristic curves 19 a to 19 d, an amount of additional power matched to the power capacity of the gear concerned is in each case supplied by the drive machine 2 to the vehicle transmission 3. Accordingly, in any operating condition the vehicle can be operated at the limit of its power without overloading the components of the vehicle transmission 3.

FIG. 4 is based on the operating situation in which one of the gear-specific power take-off torque characteristic curves 20 a to 20 d is used for the control of the drive machine 2. The gear-specific assignment is analogous to the assignment of the transport torque characteristic curves 19 a to 19 d to the four synchronous gears. In this case too the shape of the power take-off torque characteristic curve 20 d in the fourth synchronous gear corresponds to the course of the power take-off torque characteristic curve 20 according to FIG. 2.

As already mentioned earlier, it is also differentiated whether when the power take-off 10 is active, the vehicle is moving or at rest. In the case of a stationary vehicle, the vehicle transmission 3 is controlled or regulated in a gear-specific manner in accordance with the appropriate power take-off torque characteristic curve 20 a, 20 b, 20 c or 20 d with the application of a reduction factor. The reduction factor takes into account the differing lubrication behaviors, in that the respective gear-specific maximum torque that can be transmitted in accordance with the power take-off torque characteristic curves 20 a, 20 b, 20 c or 20 d is reduced.

In general, each synchronous gear of the vehicle transmission 3 can be extended by at least one powershiftable gear. To control the supply of power, in the sense of delivering additional power from the drive machine 2, with even greater precision and detail, a number of gear-specific torque characteristic curves, i.e. transport torque characteristic curves and power take-off torque characteristic curves, which number is increased by a factor corresponding to the number of powershiftable gears, can be stored recoverably in the memory unit 15 of the control unit 12. In that way the gear-specific supply of operating-situation-dependent additional power by the drive machine 2 can be regulated in a more precise manner.

INDEXES

-   1 Drive-train -   2 Drive machine -   3 Vehicle transmission -   4 Input shaft -   5 Output shaft -   6 Output shaft -   7 Differential -   8 Driven axle -   9 Wheel drive -   10 Power take-off -   11 Sensor -   12 Control unit -   13 Sensor signal -   14 Computer unit -   15 Memory unit -   16 Control signal -   17 Motor characteristic curve -   18 Normal torque characteristic curve -   19 Transport torque characteristic curve -   19 a Transport torque characteristic curve -   19 b Transport torque characteristic curve -   19 c Transport torque characteristic curve -   19 d Transport torque characteristic curve -   20 Power take-off torque characteristic curve -   20 a Power take-off torque characteristic curve -   20 b Power take-off torque characteristic curve -   20 c Power take-off torque characteristic curve -   20 d Power take-off torque characteristic curve 

1-10. (canceled)
 11. A method for operating a drive-train (1) of a vehicle which has at least one drive machine (2), a vehicle transmission (3) with at least two gears, at least one driven axle (8) and at least one power take-off (10), the method comprising: supplying a normal power level by the drive machine (2), which is controlled or regulated in accordance with a normal torque characteristic curve (18), supplying, in an operating-situation-dependent manner, additional power to at least one of the at least one driven axle (8) and the at least one power take-off (10), and controlling or regulating the additional power supplied in accordance with operating-situation-dependent torque characteristic curves (18, 19 a to 19 d, 20 a to 20 d) which are called up as a function of which one of the at least two gears is selected at the time.
 12. The method according to claim 11, further comprising monitoring activation of the at least one power take-off (10) and a driving speed of the vehicle for the operating-situation-dependent supply of additional power.
 13. The method according to claim 11, further comprising, in an operating situation of the vehicle in which the at least one power take-off (10) is not active and the vehicle is being driven at a driving speed below a driving speed limit, controlling or regulating the drive machine (2) in accordance with the normal torque characteristic curve (18) regardless of which of the at least two gears is selected at the time.
 14. The method according to claim 11, further comprising, in an operating situation of the vehicle in which the at least one power take-off (10) is not active and the vehicle is being driven at a driving speed above a driving speed limit, controlling or regulating the drive machine (2) in accordance with a gear-specific transport torque characteristic curve (19 a to 19 d) as the operating-situation-dependent torque characteristic curve.
 15. The method according to claim 11, further comprising, in an operating situation of the vehicle in which the at least one power take-off (10) is active and the vehicle is being driven at a driving speed below a driving speed limit, controlling or regulating the drive machine (2) in accordance with a gear-specific power take-off torque characteristic curve (20 a to 20 d) as the operating-situation-dependent torque characteristic curve.
 16. The method according to claim 15, further comprising, in an operating situation of the vehicle in which the at least one power take-off (10) is active and the driving speed is zero, controlling or regulating the drive machine (2) in a gear-specific manner in accordance with the power take-off torque characteristic curves (20 a to 20 d) with an application of a reduction factor.
 17. The method according to claim 11, wherein the vehicle transmission (3) has at least two synchronous gears and at least two powershiftable gears, and when these are selected, an operating-situation-dependent and gear-specific torque characteristic curve (18, 19 a to 19 d, 20 a to 20 d) is called up for the control or the regulation of the drive machine (2).
 18. A control unit (12) for the control of a drive-train (1) of a vehicle having at least one drive machine (2), a vehicle transmission (3) with at least two gears, at least one driven axle (8) and at least one power take-off (10), the drive machine (2) supplying a normal power level which is controlled or regulated by the control unit (12) in accordance with a normal torque characteristic curve (18), the drive machine (2), in an operating-situation-dependent manner, supplying additional power to at least one of the at least one driven axle (8) and the at least one power take-off (10), and the control unit (12) being designed to control or regulate the supply of additional power, in accordance with operating-situation-dependent torque characteristic curves (18, 19 a to 19 d, 20 a to 20 d), which are called up as a function of which one of the at least two gears is selected.
 19. The control unit (12) according to claim 18, wherein the control unit (12) is designed to carry out a method comprising: supplying a normal power level by the drive machine (2), which is controlled or regulated in accordance with a normal torque characteristic curve (18); supplying, in an operating-situation-dependent manner, additional power to at least one of the at least one driven axle (8) and the at least one power take-off (10); controlling or regulating the additional power supplied in accordance with operating-situation-dependent torque characteristic curves (18, 19 a to 19 d, 20 a to 20 d) which are called up as a function of which one of the at least two gears is selected at the time; and monitoring activation of the at least one power take-off (10) and a driving speed of the vehicle for the operating-situation-dependent supply of additional power.
 20. The control unit (12) according to claim 18 in combination with a computer program product with program code means which is run on the control unit to carry out a method for operating the drive-train (1) of the vehicle including steps of: supplying the normal power level by the drive machine (2), which is controlled or regulated in accordance with the normal torque characteristic curve (18); supplying, in an operating-situation-dependent manner, the additional power to at least one of the at least one driven axle (8) and the at least one power take-off (10); controlling or regulating the additional power supplied in accordance with the operating-situation-dependent torque characteristic curves (18, 19 a to 19 d, 20 a to 20 d) which are called up as a function of which one of the at least two gears is selected at the time; and monitoring activation of the at least one power take-off (10) and the driving speed of the vehicle for the operating-situation-dependent supply of additional power. 